Hi Jon,
> limitation on how much IMD performance a receiver needs is how much phase
> noise exists from other transmissions on the band. I've heard a number of
> FT1000s on the band that weren't too good - this on CW. So that could be a
> limit. Fortunately, tube PAs aren't generally too bad for wideband noise,
> but the wideband noise from
>
> some solid state drivers leaves a lot to be desired.
It's the 1000MP that has the bad TX phase noise, I can tell you that
after listening to many rigs on 160 meters while trying to work
weak DX signals close by.
Other rigs have other problems.
The 775DSP transmits on both VCO frequencies at once, and also
receives on both VCO's at once even with the second VFO turned
off according to the front panel. The closer the VCO's to the same
frequency, the stronger the spur.
Other rigs click on split because the VCO's are still settling in
while the rig goes into transmit.
I measured an old Collins KWM-2 and IMD was 50 dB below one
tone in a two tone test almost independent of drive. The same test
on a 751A produced IMD 29 dB below one tone at optimum drive,
and worse IMD performance as power was raised or lowered!
Does anyone know why the ARRL started using dB below PEP
instead of dB below one tone, like the commercial folks use? Did it
have anything to do with the poor TX IMD performance of the KWM-
380 and other solid state rigs, to make them look acceptable?
73, Tom W8JI
w8ji@contesting.com
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